The recent emphasis in the development of clinical chemistry technology has been directed toward the development of systems for "real time" analysis of biological fluids or those analyses which can be performed in the close proximity of the patient e.g., at the bedside or in the physician's office. Such biological fluids include urine, plasma, serum, and preferably, whole-blood. Clear benefits are achieved if the chemical information required by the physician is obtained during patient consultation and not several hours or days afterward. Although progress has been made toward achieving such a goal, many problems still remain including the limitations of established manufacturing methods to mass-produce electrochemical devices with sufficiently uniform performance characteristics and extended shelf-lives. Of particular interest is the lack of adequate computational techniques which minimize the time required to obtain useful information from such electrochemical devices.
To date, fluid analysis has been carried out using many types of electrochemical sensors in which potentiometric, amperometric or conductimetric measurements are performed in a steady-state or kinetic (e.g., initial rate) mode. Electrochemical sensors employed for these measurements usually consist of a two-component assembly in which a sensitized membrane is interposed between the fluid and an underlying electrode. Some membrane compositions have distinctive species recognition capabilities which enable the electrochemical sensor to detect the analyte of interest specifically and measure its concentration in a complex biological fluid. To date, however, size, complexity and expense limitations, combined with a high incidence of error resulting both from instrument quality control and accidental errors by the operator, have impeded wide spread use of this technology in locations, such as the emergency room and the doctor's office, which are remote from the central clinical chemistry laboratory. Moreover, most analytical test methods currently in use are overly cumbersome or complex. More significantly, the response of the electrochemical device, itself, may be so slow as to make such "real time" analysis very difficult. It should be noted that the concentration of certain components, such as glucose and potassium ion, in a biological fluid (e.g., whole-blood) may change significantly over a prolonged period. The change arises likely from hemolysis of related metabolic processes.
As mentioned previously, a principal obstacle against the successful implementation of "real time" clinical fluid analysis is the lack of reliable sensor manufacturing methods. Equally lacking, however, are data acquisition and manipulation methods which allow the quick retrieval of information from existing chemical sensing devices some of which are stored substantially dry in order to maximize shelf-life. The prevailing standard practice dictates that these "dry-stored" devices be allowed to reach a fully equilibrated "wet-up" state before meaningful sensor data can be recorded.